The invention relates to a system and a method for stereoscopic image display as well as to a holographic screen.
It is generally known that spatial images of objects can be generated on image areas using holographic and stereoscopic methods.
With holography, it is possible to store the entire information using the amplitudes and phases of light-waves originating from an object, and thus, the information regarding its spatial shape, as a two-dimensional grid structure in a hologram film.
The waves that originated from the object and that also contain as image information the spatial structure of the object can now be reproduced as an image area by the diffraction of a projection beam onto the grid structure of the film.
With stereoscopy, the spatial structure is recorded using conventional photography of the object from different directions that correspond, for example, to the distance between the eyes of the viewer. For the spatial impression of the images of an object to be projected onto a screen to come into existence, it has to be ensured that the left eye sees only the left image and the right eye only the right image. As is known, this is made possible either by both images being vertically polarized to one another or by having the images projected onto the screen in rapid succession with a time shift. In order to see the image spatially, the viewer must wear eyeglasses; in the first case, with glasses that allow waves to pass that are polarized vertically left and right to one another, and in the second case, with glasses that are equipped with time-controlled shutters that open synchronously with the image, alternating for light passage on the left and the right eye.
With auto-stereoscopy, one can forego the stereo eyeglasses because the different images for the left and the right eye are carried out by narrowing the angle of the light emission from the screen. However, this requires that the eyes view the image at a particular distance from the screen, or that the eye position in relation to the screen is continuously monitored and that the emission characteristic is readjusted according to the eye position of the viewer, which requires a significant effort.
The holographic method that enables a spatial view of objects in various perspectives over a wide range of angles both in the horizontal and vertical direction has the disadvantage that there is a very high information density in the hologram. It is greater by a factor of 1000 compared to a typical two-dimensional display on current screens. The technology of a three-dimensional electronic display of holographic moving images is, therefore, not yet mastered.
Stereoscopy and auto-stereoscopy enable spatial images only in the horizontal plane and viewing of the object only from a fixed viewing angle. The autostereoscopy is a very involved method and is only employed for individual viewers in close proximity to the screen with a defined head distance and head position. On the other hand, the stereoscopy using stereo eyeglasses could be realized in various versions, for example, in film technology for full-color slide projection and in 3-D movie theaters, as well as in the electronic image technology for visualizing 3-D graphics and 3-D videos. This is due to the simple technical implementation and the limited number of additional requirements with regards to information density, which here is greater by a factor of 2 when compared to a typical two-dimensional image display. Despite the limitation of a stationary viewing location and viewing angle, the stereoscopic image generation is widely used in the entertainment industry and in simulation technology. Using fast, modern computers and motion sensors that continuously register the viewer""s body and head movements as well as a corresponding image adaptation in the computer, a spatial impression of the environment and the objects (virtual reality) can be generated in all directions using stereoscopic projection. Using sensor gloves that are connected to the computer, the viewer can then interact with the objects and functions of this virtual world.
With these latest new achievements of electronic stereoscopic image display, a broad field of application has been developed for this technology in a short time, despite the handicap of wearing polarization eyeglasses (shutter glasses). Among these applications are training of surgeons using virtual operations, astronauts assembling virtual spatial structures, training of vehicle conductors and airplane pilots, and dynamic visualization of the outside and inside of virtual buildings and vehicles, which is important for architects or vehicle designers and their customers.
In contrast to the holographic and the auto-stereoscopic image display, which will only achieve the required technical development and cost advantages in the distant future, a very rapid distribution of the electronic stereoscopic image display in conjunction with the development of powerful image computers is to be expected in the near future for a broad spectrum of applications.
Currently, however, the stereoscopic projection still suffers from numerous problems and disadvantages. Primarily, these problems are low sensitivity, lack of image sharpness, low image contrast and inadequate color fidelity in relation to external light. It is generally known that a good image quality for slide presentations or in a movie theater is achieved only in darkened rooms. Any external light will also be rayed to the viewer from the screen, and is added to the effective light portion of the image, which leads to a lower contrast and reduction in the color saturation.
A second problem is the mutual interference of the images during projection. This is especially the case with concave screens that are used to fill the visual field of the viewer as much as possible, or in closed projection rooms with screens on all sides around the viewer, the so-called xe2x80x9ccavesxe2x80x9d for the image display of the virtual reality. In these situations, the light from one side of the screen is scattered to the other side and is added to the effective light of the image, causing the same reduction in quality as with additional daylight.
It is the objective of the invention to enable a stereoscopic image display that ensures a high image quality especially for moving images and that can be realized easily and cost-effectively.
The system for stereoscopic image display subject to the invention includes a projection device for the projection of two images with different perspectives, a projection screen to reproduce the images, and a device for the separate viewing of the two images with the left eye and the right eye, where the projection device includes means for generating projection beams with differing polarization directions, and where the projection screen is a holographic screen with a grid structure that causes two differently polarized images to be generated when struck by light beams with two different polarization directions. This results in a high image contrast with high color fidelity for the stereoscopic display. Especially, a cross-interference of various image portions is avoided, because only the light coming from the projection device is reflected by the respective image point.
The holographic screen subject to the invention for the stereoscopic image display includes a hologram, whose grid structure corresponds to a hologram recording of an actual screen, where the grid structure corresponds to a hologram recording with a defined polarization direction or several hologram recordings with two polarization directions that are perpendicular to one another. In this manner, it is particularly well suited for the stereoscopic image projection or reproduction, whereby a high image quality is achieved.